The invention relates to the field of video imaging and, more particularly, to the field of MOS imaging devices.
In the past, video imaging has been done by several different types of sensors including the image orthicon vacuum tube. These devices were expensive and bulky and were subject to damage under certain conditions such as when the camera is pointed directly at the sun.
To overcome some of these problems, a search began for an integrated circuit imaging device. With the advent of metal-oxide-semiconductor (MOS) technology for integrating active devices such as transistors and photodiodes onto a silicon substrate, MOS imaging devices were developed. The structure and architecture of these devices is, by now, well-known. For example, a solid state image pickup device having photoelectric elements each of which includes an MOS field effect transistor is taught in U.S. Pat. No. 4,143,389. An improved version of this cell is taught in U.S. Pat. No. 4,155,094 wherein a PN diode is used to create the photoelectric effect hole-electron pairs and an MOS diode is used to store the charge so generated. An architecture for reading out the data from an array of such cells is taught in U.S. Pat. No. 4,316,205. The '205 patent teaches vertical and horizontal switching transistors which address the photodiodes and shift registers which constitute vertical and horizontal scanning circuits for turning the switching transistors on and off. Another architecture wherein charge transfer devices are used for the vertical and horizontal scanning circuits is taught in U.S. Pat. No. 4,349,743.
Hitachi Ltd. of Japan recently announced a color MOS imager in a paper by M. Aoki, H. Ando, S. Ohba, I. Takemoto, S. Nagahara, T. Nokano, M. Kubo and T. Fujita entitled "2/3 Format MOS Single Chip Color Imager", published in the IEEE proceedings of the Electron Devices Meeting of August, 1980, Vol ED 27, #8, pp. 1676-1687. This device utilized four primary color video signal outputs from each of four pixel elements arranged into square areas on the substrate. One horizontal and one vertical shift register is used for reading data from the array.
Hitachi also manufactures another MOS imager under the part designation HE 98222 which has an organization partially similar to that of the invention. However, this part is only capable of black and white video signal generation because of its organization which provides only two output lines.
Major modifications would have to be made to both the HE 98222 and the structure taught in the paper by Aoki et al to achieve the option of either monochrome or color operation in the variety of interlace and non-interlace modes available when using the structure of the invention. Color signals require three separate video output signals from a matrix of many cells where each cell is comprised of three different color filtered light sensing areas of the substrate. In contrast, black and white imagers need only two output lines. Further, some applications for video imagers require that the video signals be read out from the imager in either an interlace, a non-interlace or a pseudo-interlace mode.
Thus, a need has arisen for a solid state imaging device that cannot be damaged by inadvertent overexposure as by accidently pointing the camera at the sun. Further, there is a need for such a device which has the flexibility to be easily adapted to either color or black and white applications in either interlaced, non-interlaced or pseudo-interlaced format.